265/70/17 tires better than 255?

i have an 07 f150 4x4 and am lookin to buy new tires for it. it came stock with 255 tires on them but the tires i want and are about 40 dollars/ tire cheaper so its an obvious choice what to get. im not worried about a speedo difference since i am getting it reprogrammed. but will i lose mpg or acceleration with the bigger tires?